Tube treating and method

ABSTRACT

Synthetic resinous thermoplastic tubing is reduced radially in diameter with minimal increase in length by passing the tube through a plurality of successively smaller dies wherein a minor portion of the die moves relative to a major portion of the die during the reduction step. Plastic tube is obtained which has a tendency to expand radially with a minimal alteration in its length. Such tubing is particularly suitable for lining of pipe.

Plastic lined pipe finds wide application in a variety of applications.Such pipe beneficially is chemically resistant to many materials whichare processed and, in general, is easily installed and has the addedadvantage of being more resistant to impact than piping such as glass,ceramic or the like. Many thermoplastic materials are employed to linepipe. The particular thermoplastic selected is usually dependent on theintended service. Oftentimes when a thermoplastic lined pipe has been inservice for a period of time, fracture of the liner occurs at a locationgenerally adjacent the one or the other of the terminal flanged ends.Such failure is oftentimes considered to be due to undesired residualmolecular orientation in the plastic liner. In order to minimize suchresidual orientation or tendency of the liner to shrink when exposed totemperature near the upper service temperature limit of the pipe, someplastic lined pipes have been prepared by the process of swaging themetallic outer casing over a plastic liner. The swaging may be continueduntil the liner is firmly lodged within the metallic casing and themetallic casing has reached a standard size.

Other methods of lining a pipe include stretching of an oversizedplastic liner to reduce its diameter, inserting the stretched liner in apipe, removing the tension on the liner and permitting the liner toexpand and contact the inner wall of the casing. Some plastic lineconduit is prepared by placing an undersized liner within a casing,heating the liner and inflating the liner with liquid or gas pressureuntil the liner contacts the inner wall of the casing. Such procedures,although satisfactory for many purposes, are generally not believed toprovide conduit having optimum properties for the materials employed.

It would be desirable if there were available an improved method for thepreparation of plastic tubes.

It would also be desirable if there were available an improved methodfor the preparation of plastic tubes which had been radially reduced indiameter without generally altering the length thereof.

It would also be desirable if there were available an improved methodfor the preparation of plastic lined conduit.

These benefits and other advantages in accordance with the presentinvention are achieved in a method of preparing a synthetic resinoustube comprising preparing a synthetic resinous tube, the steps of themethod comprising providing a synthetic resinous thermoplastic tubehaving a diameter greater than the desired diameter introducing aportion of the tube into a plurality of die plates having successivelysmaller circular openings therein. The tube having a region of decreaseddiameter generally adjacent the die plate having the smaller opening anda region of major diameter generally adjacent the die plate having thelargest opening, moving at least one of the die plates towards theregion of major diameter thereby reducing the diameter of a portion ofthe tube while maintaining the conduit in fixed relation to at least amajor portion of the remaining die plates. Subsequently, in sequence,moving each said plurality of die plates in the hereinbefore describedmanner to provide a synthetic resinous thermoplastic tube having reduceddiameter, the foregoing steps being performed at a temperature betweenthe glass temperature of the resinous tube and the softeningtemperature.

Particularly suitable for the practice of the present invention is atube diameter reducing apparatus. The tube diameter reducing apparatuscomprises in cooperative combination a frame, the frame having alongitudinal axis, a plurality of die plates within the frame andselectively portionable therein, the die plates each defining a tubereceiving opening of generally successively decreasing diameter, theopenings of the die plates being disposed in planes generally normal tothe longitudinal axis, the openings of the die plates being generallycoaxially disposed, means to selectively position the die plates alongthe axis of the frame, and provide sequential movement of a minorportion of the die plates relative to a major portion thereof,subsequently moving each of the die plates in such a manner.

Also, contemplated with the scope of the present invention is a methodfor lining conduit which comprises providing a conduit to be lined. Theconduit to be lined having a generally cylindrical passage therein,providing a synthetic resinous thermoplastic tube having an outsidediameter greater than the diameter of the cylindrical passage reducingthe outside diameter of the resinous tube in the hereinbefore describedmanner to a diameter which is sufficiently small to permit entry of theplastic tube into the conduit, inserting the plastic tube into theconduit and causing the tube to expand and contact at least a portion ofthe inner wall defining the conduit passageway.

Further features and advantages of the present invention will becomemore apparent from the following specification when taken in connectionwith the drawing wherein:

FIGS. 1 through 3 schematically depict portions of the process inaccordance with the invention;

FIG. 4 is a schematic representation of the function of an apparatussuitable for the practice of the present invention;

FIG. 5 is a sectional view of the assembly of FIG. 4 taken along theline 5--5 thereof;

FIG. 6 is a schematically plan view of a simplified apparatus;

FIG. 7 is a sectional view of the apparatus of FIG. 6;

FIG. 8 is a schematic representation of operating cam employed in theapparatus of FIGS. 6 and 7.

In FIG. 1 there is schematically depicted an assembly generallydesignated by the reference numeral 10 which assists in illustrating theprocess of the invention. The assembly 10 comprises a synthetic resinousthermoplastic tube 11. The tube 11 has a region of major diameter 12 anda region of minor diameter 13 remotely disposed therefrom. Disposedbetween the region of major diameter 12 and the region of minor diameter13 are a plurality of die plates 15, 16, 17, 18 and 19. Each of the dieplates 15 through 19 have decreasing die orifices designated by thecorresponding number followed by the suffix "a". The orifices 15athrough 18a are of successively decreasing diameter and each has agenerally frustoconical configuration. Initially placing the tube 11within the die plates 15 through 19, the largest die plate 15 is forcedover the tube and the die plates having successively smaller openingsare in turn positioned on the tube.

In FIG. 2 the die plate 15 partly reduces the diameter of the tube overthe region through which it has been moved. The remaining die plates 16,17 and 18 remain fixed relative to the tube and retain the tube 11frictionally therein.

In FIG. 3 the die plates 15, 17, 18 and 19 have been maintained fixedrelative to the tube and the die plate 16 moved toward the die plate 15while the tube 11 is frictionally retained within the openings of thedies 15, 17, 18 and 19. Thus, by successively advancing one of the dieplates and maintaining the remaining die plates in a fixed position thediameter of the tube is reduced from the diameter of the portion 12 intothe portion of the diameter 13 without introducing longitudinal stretchor orientation into the plastic tube.

In FIGS. 1 through 3 the assembly has been shown employing five dieplates. Five die plates are used for purpose of illustration. For mostplastic tubes it is desirable to employ ten or more die plates in orderto maintain adequate frictional engagement of the tubes by the "fixed"die plates.

FIG. 4 depicts a partly sectioned cut-away schematic representation ofthe principal functional parts of an apparatus for the practice of theinvention. The apparatus of FIG. 4 is generally designated by thereference numeral 25. The apparatus comprises a frame (not shown) whichsupports a rotatable cam 26 having a generally circumferential camminggroove 27. The cam 27 is of generally hollow cylindrical configurationand has affixed thereto a drive gear 28 which in turn is in operativecombination of a drive gear or spur gear 29 rotated by a motor 30. Asynthetic resinous thermoplastic conduit 31 is disposed within the cam26 but not in contact therewith. A plurality of die plates 33, 34, 35,36 and 37 are disposed generally adjacent to the cam 26 and arecoaxially disposed relative thereto. Each of the die plates 33 through37 have openings of successively decreasing diameter in the mannersimilar to the openings of die plates 15 through 19 of FIGS. 1 through3. A die plate positioning rod 34a is in operative communication withthe camming groove 27 and the die plate 34. Similarly, a positioning rod36a is in operative combination with die plate 36 and the camming groove27 of the cam 26. On rotation of the cam 26 the positioning rod 34a andassociated positioning rods 33a, 35a, 36a and 37a (not shown) move thedie plate in a manner as generally illustrated in FIGS. 1 through 3.

In FIG. 5 there is a schematic representation of a view of a device suchas that as depicted in FIG. 4 showing the location of die plateoperating rods 33a through 37a. The cam 26 has a single step cam groove27 disposed therein, that is, for each rotation of the cam 26 anoperating rod such as the operating rod 34a is slowly pushed toward thesmaller end of conduit 31 and rapidly drawn toward the major end ofconduit 31. Thus, four of the five operating rods as depicted in FIG. 5move slowly away from the cam 26 and one is moved relatively rapidlytoward the cam 26 bringing with it its associated die plate. Thus, thefive die plates 33 through 37 as depicted in FIG. 4 most of the timeduring the rotation of the cam 26 moves slowly away from the cam whilethe die plate which encounters the step 27a in the camming groove 27 isdrawn toward the cam providing incremental reduction in the diameter ofthe tube.

In FIG. 6 there is a simplified schematic representation of a practicalapparatus for the practice of the present invention generally designatedby the reference numeral 40. The apparatus 40 comprises a frame 41. Theframe 41 has a first or inlet end member 42 and a second or dischargeend member 43. The end members 41 and 42 are affixed to each other by alongitudinal frame member 44. A bearing 45 slidably engages thelongitudinal frame member 44. A mounting bracket 46 is rigidly affixedto the bearing 45. The first end member 42 has rotatably affixed theretoa hollow cam member 46 of the general configuration cam member 26 ofFIG. 4. The cam member 46 is rotated by a rotating means (not shown).Within the frame 41 are disposed die plates 48, 49, 50 and 51. The dieplates 48 through 51 are arranged in a manner generally as the dieplates of FIGS. 1 through 4 and have successively smaller openings asthey become more remote from the first end 42. A second set of dieplates 48a, 49a, 50a and 51a are disposed adjacent the discharge end 43and the openings in the die plates 48a through 51a are smaller than theopenings in the die plates 48 through 51 and decrease in diameter towardthe discharge end 43 of the frame 41. The openings of the die plates 48through 51 and 48a through 51a are generally coaxially arranged. Threedie plate actuating rods 48' engage die plates 48 and 48a by means ofnotches formed in both the die plates and the actuating rods. Each ofthe actuating rods has disposed thereon a cam follower 48" which engagesan outwardly disposed generally annular camming groove 53 formed in theouter surface of the cam 46. Similarly actuating rods 49', 50' and 51'support the die plates 49 through 51 and 49a through 51a. The die platesas shown in FIG. 7 have a generally triangular configuration wherein thedie plates are supported by the actuating rods.

In FIG. 8 there is schematically depicted the configuration of thegroove 53 of the cam 46. The groove 53 is a three cycle groove, that is,three cycles per 360° rotation of the cam and of such configuration thatthe actuating rods 48' through 51' are moved slowly away from the framemember 42 and subsequently rapidly returned toward the frame member 42,thus, as illustrated in FIGS. 6 and 7, three of the die plates remainfixed relative to one another while the fourth plate moves.

Apparatus generally as shown in FIGS. 6-8 but having ten plates per dieplate group and three die plate groups provides a convenient means ofreducing the diameter of deformable plastic tubes without causingincrease in length.

A wide variety of thermoplastic resinous compositions are useful in thepractice of the present invention including polyperfluorocarbons such aspolytetrafluoroethylene, polychlorotrifluoroethylene;polyhalohydrocarbons such as polyvinylfluoride; vinylidene chloridepolymers such as sarans, vinylidene chloride-ethyl acrylate copolymers;polyvinyl chloride; polyolefins such as polypropylene, polyethylene,resinous polymers of ethylene and propylene; nylon 6, nylon 66, nylon 7and the like; alkenyl aromatic polymers including styrene polymers suchas rubber-modified polystyrene, styrene-acrylonitrile; polyethers suchas polymers of 2,2-bis(chloromethyl)oxacyclobutane. Oftentimes if thetube has been reduced in diameter at room temperature, the tube may beplaced within the rigid outer casing, warmed slightly to causeaccelerated expansion and provide a lined conduit in which the liningtightly engages the rigid outer housing.

For many purposes, the expansion of the conduit due to plastic memory isadequate to retain the liner within the outer casing, such as a steelpipe, under service requirements. If it is anticipated that there willbe a significant tendency of the liner to be subject to repeatinglongitudinal stresses wherein movement is undesirable, generally a linerwith larger initial diameter will be employed together with a greaterdegree of reduction of diameter of the liner.

Beneficially, if desired, a button or tapered plug may be forced throughthe lined tube to cause the liner to further expand and deform itnoimperfections within the conduit wall to provide a lined pipe which willshow maximum resistance to molding under an axially applied force.

Lined conduit prepared in accordance with the present inventionmaintains the liner under circumferential and longitudinal compressiveforces which substantially reduces the possibility of stress cracking ofthe liner as well as longitudinal movement.

The precise number of die plates employed in the practice of theinvention will vary depending upon the lubricity of the surface of theparticular liner used, the degree of the reduction desired and thetemperature of diameter reduction. For most synthetic resinous linersnot more than 20 percent and preferably 10% of the die plates shouldmove at any one time relative to the remaining die plates which do notmove relative to one another. Generally the orifice in the die plates isprovided with a generally frustoconical configuration and a sharptrailing edge. By trailing edge is meant each of the die plate orificesadjacent the discharge end of the apparatus and advantageously anoutwardly flaring or belled forward edge which facilitates the entranceof a lined conduit into the die plate opening while the sharp trailingedge serves to grip the conduit and prevent motion of the conduittowards the leading edge of the die opening.

The method and apparatus of the present invention are successivelyemployed to reduce the diameters of synthetic resinous tubes of thehereinbefore delineated resins in a highly satisfactory manner.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in thehereto-appended claims.

What is claimed is:
 1. A method for the preparation of a syntheticresinous tube capable of radial expansion and generally without changeof length of the tube upon expansion, the steps of the methodcomprisingproviding a synthetic resinous thermoplastic tube having adiameter greater than a desired diameter, introducing a portion of thetube into a plurality of die plates having successively smaller circularopenings therein, the tube having a region of decreased diametergenerally adjacent the die plate having the smaller opening and a regionof major diameter generally adjacent the die plate having the largestport opening, moving at least one of the die plates towards the regionof major diameter thereby reducing the diameter of a portion of the tubewhile maintaining the conduit in fixed relation to at least a majorportion of the remaining die plates, subsequently, in sequence, movingeach said plurality of die plates in hereinbefore described manner toprovide a synthetic resinous thermoplastic tube having reduced diameter,the foregoing steps being performed at a temperature between the glasstemperature of the resinous tube and the softening temperature.
 2. Themethod of claim 1 wherein not more than 10 percent of the die plates aremoved toward the region of major diameter.
 3. The method of claim 1including a plurality of sets of die plates each having openings ofdecreasing diameter are employed and not more than 10 percent of each ofthe sets is moved relative to the remaining portion of the sets.
 4. Themethod of claim 1 wherein the die plates have openings of generallyfrustoconical configuration.
 5. The method of claim 1 including the stepof disposing the reduced diameter of plastic conduit within a rigidouter casing and causing the plastic conduit to expand and contact theouter casing.